JP6760417B2 - Manufacturing method for hot press dies, hot press equipment and hot press molded products - Google Patents

Description

The present invention relates to a hot press die, a hot press device, and a method for manufacturing a hot press molded product. Specifically, the top plate, a ridge line continuous with the top plate, and a vertical wall continuous with the ridge line. The present invention relates to a technique for suppressing cracking of a vertical wall in the case of producing a hot press-formed product having a cross section having a cross section (for example, a hat cross section or a grooved cross section).

In recent years, in order to reduce the weight of automobiles, it has been promoted to increase the strength of steel materials and reduce the weight used. In thin steel sheets widely used in automobiles, as the strength increases, the press formability decreases, and it becomes difficult to manufacture a complicated shape. Specifically, in a high-strength blank, the ductility is lowered and breakage occurs at a portion having a high degree of workability, springback and wall warpage are increased, and the dimensional accuracy of the press-formed product is deteriorated. Therefore, it is not easy to cold press-mold a blank made of a steel plate having a high strength, particularly a tensile strength of 780 MPa class or higher, to produce a press-formed product having a desired shape. Although high-strength steel sheets can be processed by roll forming instead of press forming, only parts having a uniform cross section in the longitudinal direction can be produced.

On the other hand, Patent Document 1 discloses a method called hot press forming in which a blank made of a heated steel sheet is press-formed, and Patent Document 2 discloses after preforming the blank into a predetermined shape at room temperature. A hot press forming method (pre-press quenching method) that simultaneously achieves high strength and formability of a steel sheet by heating to an austenite region and quenching in a press forming die is disclosed.

In hot press forming, the steel sheet at the time of forming is hot, soft and highly ductile, so that it is possible to manufacture a press-formed product having a complicated shape with good dimensional accuracy. Further, by heating the steel sheet in the austenite region and quenching (quenching) it in the press forming die, the strength of the steel sheet due to martensitic transformation can be increased at the same time.

As described above, although the degree of freedom of forming a high-strength steel sheet is greatly increased by hot press forming, cracks may occur during press forming even if hot press forming is performed.

FIG. 8 (a) is a perspective view showing a hot press-formed product 1 in which such cracks occur, and FIG. 8 (b) shows a 1/2 cross section of the press forming apparatus 3 of the hot press-formed product 1. It is explanatory drawing which shows. Further, FIG. 9A is a perspective view showing a hot press-molded product 2 that causes similar cracks, and FIG. 9B is a half cross section of the press-molding apparatus 4 of the hot press-molded product 2. 9 (c) is an explanatory view showing a cross section corresponding to the AA'cross section in FIG. 9 (a) in the press molding apparatus 4 before the start of press molding. The two straight lines in FIGS. 9 (a) and 9 (c) indicate that the positions indicated by each are the corresponding positions before and after press molding.

As shown in FIG. 8 (b), the blank 8 is hot press-formed by drawing using the punch 5, die 6 and blank holder 7 of the press forming apparatus 3, and as shown in FIG. 8 (a). For example, a cross section having a top plate 1a, two ridges 1b, 1b continuous with the top plate 1a, and two vertical walls 1c, 1c continuous with the two ridges 1b, 1b, respectively (for example, a hat cross section or a groove). In the case of manufacturing a hot press-molded product 1 having a curved portion 1d having a mold cross section) and having a curved portion 1d having a curved ridge line 1b protruding outside the top plate 1a in a plan view in the pressing direction on the top plate 1a. Cracks are likely to occur during hot press forming on the vertical wall 1c continuous with the top plate 1a of the portion 1d.

Further, as shown in FIGS. 9 (b) and 9 (c), the blank 8 is hot press formed by bending using the punch 5 and the die 6 of the press forming apparatus 3, and FIG. 9 (a) is shown. As shown in, for example, a cross section having a top plate 2a, two ridges 2b and 2b continuous with the top plate 2a, and two vertical walls 2c and 2c continuous with the two ridges 2b and 2b (for example). When manufacturing a hot press-molded product 2 having a hat cross section or a groove-shaped cross section and having a step 2e on the top plate 2a in the pressing direction (direction orthogonal to the top plate 2a), the top plate near the step 2e Cracks are likely to occur during hot pressing on the vertical wall 2c continuous with 2a (particularly the top plate 2a existing at a low position with the step 2e as a boundary).

Many inventions have been proposed for the purpose of preventing cracking of press-formed products. Patent Document 3 discloses a method for manufacturing a cold press-molded product of a cross-section hat-shaped member curved in a plan view in a line of sight orthogonal to the top plate, and Patent Document 4 discloses a cross-section hat by hot press molding. A method of incorporating an arc-shaped separate punch in a mold (punch) when molding a member of a mold and operating the separate punch at the bottom dead point of molding is disclosed. Further, Patent Document 5 discloses that in a molding process. A hot press forming method by draw forming which improves moldability by cooling a specific part of a material with a cooling catalyst is disclosed.

UK Patent Publication No. 1490535 Japanese Unexamined Patent Publication No. 10-96031 International Publication No. 2014-106923 Pamphlet Japanese Unexamined Patent Publication No. 2015-2015 Japanese Unexamined Patent Publication No. 2014-208374

However, when the manufacturing method disclosed in Patent Document 3 is applied to hot press molding, cracks may occur in the punch shoulder portion.

The method disclosed in Patent Document 4 cannot suppress the cracking of the vertical wall that occurs before reaching the bottom dead center of molding. Further, in order to operate the separate punch, it is necessary to separately provide an operating device for the separate punch, and the cost of the device cannot be denied.

Further, although Patent Document 5 does specify a method for suppressing cracking of the vertical wall, an increase in device cost is unavoidable even with this method.

As described above, in the conventional technique, it is not possible to suppress the cracking of the vertical wall due to the elongation strain generated in the vertical wall during hot press forming described with reference to FIGS. 8 and 9 without increasing the manufacturing cost.

Cracking of the blank in hot press forming is often caused by a local temperature drop of the blank caused by contact between the blank and the die (punch, die). Since the temperature-reduced portion in contact with the mold in the blank has higher hardness and is less likely to be deformed than the non-temperature-reduced portion (high-temperature portion) in contact with the mold in the blank, strain is concentrated on the non-temperature-reduced portion during molding. Will be done.

As a result of diligent studies to solve the above problems based on such a premise, the present inventors have obtained the findings A to K listed below and completed the present invention.

(A) FIG. 10 (a) is a contour by numerical analysis of the plate thickness reduction rate at the bottom dead center of molding in the hot press molded product 1 hot press molded by the press molding apparatus 3 shown in FIG. 8 (b). 10 (b) is a diagram showing the temperature of each part at a position 10 mm above the bottom dead center of molding in the hot press molded product 1 hot press molded by the press molding apparatus 3 shown in FIG. 8 (b). It is a contour diagram by numerical analysis. The numbers in FIG. 10A indicate the plate thickness reduction rate in the indicated region.

As shown in FIG. 10A, the vertical wall 1c on the outer peripheral side of the curved portion 1d, which is prone to cracking in hot press forming, has a vertical wall 1c.
(I) The part where tension is applied not only in the pressing direction but also in the direction orthogonal to the pressing direction during molding.
(Ii) A portion that is kept at a high temperature because it does not come into contact with the molds 5 and 6, and (iii) a portion sandwiched between the die shoulder R portion and the punch shoulder R portion of the mold that the blank 8 contacts. It has the characteristic of being.

(B) From these features (i) to (iii), the vertical wall 1c on the outer peripheral side of the curved portion 1d is likely to be cracked due to a large decrease in plate thickness due to concentration of strain during molding. Therefore, in order to suppress the cracking of the vertical wall 1c, the local concentration of strain is relaxed by expanding the region of the non-temperature lowering portion (high temperature portion) of the vertical wall 1c on the outer peripheral side of the curved portion 1d. Is effective.

(C) Two ridge lines 1b and 1b continuous with the top plate 1a and two vertical walls 1c and 1c continuous with the two ridge lines 1b and 1b are attached to the top plate 1a in a plan view in the pressing direction and outside the top plate 1a. When the curved portion 1d having the curved ridge line 1b overhanging is provided, the strain is remarkably concentrated on the vertical wall 1c on the outer peripheral side of the curved portion 1d. This is because if the ridge line 1b is bent, the flow of the blank during press molding becomes non-uniform.

(D) FIG. 10 (c) is a contour diagram obtained by numerical analysis of the plate thickness reduction rate at the bottom dead point of molding in the hot press molded product 10 hot press molded by the press molding apparatus according to the present invention described later. FIG. 10D is a contour diagram obtained by numerically analyzing the temperature of each part at a position 10 mm above the bottom dead point of molding in the hot press-molded product 10 hot-press-molded by the press-molding apparatus according to the present invention. is there. The numbers in FIG. 10 (c) indicate the plate thickness reduction rate in the indicated region.

As can be understood from the comparison between FIGS. 10 (c) and 10 (d) and FIGS. 10 (a) and 10 (d), the hot press molded product 10 is manufactured by hot press molding. In this case, a punch having an inner pad attached to the top of the punch is used. Specifically, a portion of the blank that is formed into the curved portion 10d of the top plate 10a in a plan view in the pressing direction is formed on the top of the punch. By supporting with an inner pad mounted freely in and out and performing hot press forming using a punch and a die, the region of the non-temperature lowering portion (high temperature portion) of the vertical wall 1c on the outer peripheral side of the curved portion 10d is expanded. As a result, the local concentration of strain can be relaxed and the reduction rate of the plate thickness can be suppressed, so that the occurrence of cracks on the vertical wall 10c on the outer peripheral side of the curved portion 10d can be effectively eliminated.

(E) The findings of (A) to (D) above are based on the case where the top plate has only one ridgeline, that is, an annular ridgeline such as a circle, an ellipse, a polygon, etc. in a plan view in the pressing direction with respect to the blank. It can also be applied to hot press molding of the formed top plate.

(F) FIG. 5 (a) shows the dead center under molding in the hot press-molded product 2 having a step 2e on the top plate 2a, which was hot-press-molded by the press-molding apparatus 4 shown in FIGS. 9 (b) and 9 (c). FIG. 5 (b) is a contour diagram obtained by numerical analysis of the plate thickness reduction rate at a point, and FIG. 5 (b) shows a step on the top plate 2a hot press-formed by the press forming apparatus 4 shown in FIGS. 9 (b) and 9 (c). It is a contour figure by numerical analysis of the temperature of each part at the position 4 mm above the bottom dead center of molding in the hot press molded product 2 with 2e. Here, the step 2e is a boundary portion where the molding height of the top plate 2a changes.

As shown in FIG. 5A, the top plate 2a near the step 2e (the top plate 2a existing at a low position with the step 2e as the boundary, particularly the punch side at the boundary of the step 2e), which is likely to crack in hot press forming. On the vertical wall 2c continuous with the convex portion), similarly to the curved portion 1d shown in FIGS. 10 (a) and 10 (d),
(I) The part where tension is applied not only in the pressing direction but also in the direction orthogonal to the pressing direction during molding.
(Ii) It is a part that is kept at a high temperature because it does not come into contact with the dies 5 and 6, and (iii) it is sandwiched between the die shoulder R part and the punch shoulder R part of the dies 5 and 6 that the blank 8 comes into contact with. It has the characteristic of being a part.

(G) From these features (i) to (iii), the vertical wall 2c of the stepped portion 2e of the top plate 2a is likely to be cracked due to a large decrease in plate thickness due to concentration of strain during molding. The reason for this will be explained in more detail.

FIG. 6A is an explanatory view showing the shape of the blank 20 at a position 20 mm above the bottom dead center of molding when the hot press molded product 14 is molded by the press molding apparatus 12 according to the present invention. b) is an explanatory view showing a cross section of the press forming apparatus 12 at this time.

As shown in FIGS. 6A and 6B, if there is a step in the portion 8a formed on the top plate 2a of the blank 8, the portion 8a located on the convex side 5a of the punch 5 punches at the initial stage of molding. It will be restrained and molded before the portion 8b located on the concave side 5b of 5. Therefore, when the molding proceeds and the portion 8b located on the concave side 5b of the punch 5 is formed, the inflow amount of the material is increased because the portion 8a located on the convex side 5a of the punch 5 is restrained. There is a shortage, and cracks are likely to occur in the portion formed on the vertical wall 2c that is continuous with the portion 8b. In particular, in hot press forming, the non-temperature lowering portion (high temperature portion) of the portion of the blank 8 formed on the vertical wall 2c during forming becomes smaller, so that the blank 8 is more constrained than in cold press forming. The influence of the above becomes stronger, and cracks are more likely to occur in the portion formed on the vertical wall 2c, which is continuous with the portion 8b.

(H) Therefore, in order to suppress cracking at the vertical wall 2e in the hot press-formed product 2 having the step 2e on the top plate 2a, the non-temperature decrease of the vertical wall 2c continuous with the step 2e on the top plate 2a. It is effective to relax the local concentration of strain by expanding the area of the part (high temperature part).

FIG. 7A is an explanatory view showing the shape of the blank 20 at a position 20 mm above the bottom dead center of molding when the hot press molded product 14 is molded by the press molding apparatus 12 according to the present invention described later. 7 (b) is an explanatory view showing a cross section of the press forming apparatus 12 at this time.

As shown in FIG. 7B, a punch 16 having an inner pad 21 attached to the top of the punch is used, specifically, the punch 16 is formed on the top plate 14a of the hot press molded product 14 in the blank 20. By supporting the vicinity of the portion formed on the step 14e by the inner pad 21 and performing hot press forming using the punch 16 and the die 18, the portion 20a of the blank 20 located on the convex side 16a of the punch 16 Then, the portion 20b located on the concave side 16b of the punch 16 is formed substantially at the same time, and the restraint of the blank 20 at the time of forming the portion 20b is reduced.

(I) FIG. 5 (c) is a contour diagram obtained by numerical analysis of the plate thickness reduction rate at the bottom dead point of molding in the hot press molded product 14 hot press molded by the press molding apparatus according to the present invention described later. FIG. 5D is a contour diagram obtained by numerically analyzing the temperature of each part at a position 4 mm above the bottom dead point of molding in the hot press-molded product 14 hot-press-molded by the press-molding apparatus according to the present invention. is there.

As can be understood from comparing FIGS. 5 (c) and 5 (d) with FIGS. 5 (a) and 5 (b), a hot press having a step 14e on the top plate 14a by hot press forming. When manufacturing the molded product 14, a punch having an inner pad attached to the top of the punch is used, specifically, the blank is molded on the top plate 14a on the lower side with the step 14e as a boundary. The part to be formed on the vertical wall 14c near the step 14e in the blank 20 by supporting the portion to be formed by the inner pad mounted on the top of the punch and performing hot press forming using the punch and the die. Since the region of the non-temperature drop portion (high temperature portion) can be expanded, the local concentration of strain can be alleviated and the decrease in plate thickness can be suppressed, so that the occurrence of cracks in the vertical wall 14c near the step 14e is effective. Can be resolved.

(J) As described above, by using the inner pad 21, the restraint of the blank 20 at the time of molding the portion 20b is reduced, and the non-temperature lowering portion (high temperature portion) of the portion of the blank 20 formed on the vertical wall 14c. ) Is expanded, the moldability is significantly improved, and cracking at the vertical wall 14c of the 14d near the step 14e is suppressed. That is, when hot press molding is performed on the blank 20 to manufacture a hot press molded product 14 having a step in the press direction (height of the molded product 14) on the top plate 14a having a hat-shaped cross section or a groove-shaped cross section. By using the inner pad 21, it is possible to effectively suppress the occurrence of cracks in the vertical wall 14c continuous with the top plate 14a having a low height with the step 14e as a boundary.

(K) As described above, when hot-pressing a hat-shaped or groove-shaped cross section or when forming a convex portion having a top plate with respect to a blank by hot pressing, the vicinity of the punch shoulder R portion in the blank If the part formed on the vertical wall is a part where cracking is a concern due to tension being applied in the direction orthogonal to the pressing direction, the vicinity of the blank part is supported by the inner pad. However, by performing hot press molding, cracking of the blank at this site can be avoided.

The present invention is as listed below.
(1) In a hot press die provided with a punch top and a punch shoulder R portion continuous with the punch top, a predetermined amount is projected from the punch top to the outside of the punch and is arranged at the bottom dead point of molding. A hot press die characterized by having an inner pad housed in the top of the punch.

(2) The inner pad is a portion of the blank where tension is applied to a portion of the blank formed on a vertical wall in the vicinity of the punch shoulder R portion in a direction orthogonal to the pressing direction (a punch that applies tension to the blank). The hot press die according to item 1, characterized in that it is arranged in a portion).

(3) The hot press die according to item 2, wherein the portion is a portion where the edge of the punch top protrudes to the outside of the punch and is bent in a plan view in the pressing direction.

(4) The hot press according to item 2, wherein the portion is a low portion (low portion of the punch) having a low punch height with a step portion formed on the top of the punch in the punch height direction as a boundary. Mold for use.

(5) A hot pressing apparatus including the hot pressing die according to any one of items 1 to 4.

(6) The top plate and the top plate are formed by press-molding the heated blank using the punch and die, which are the hot press dies described in any one of items 1 to 4. A method for producing a hot press-molded product having a cross section having a ridge line continuous with a plate and a vertical wall continuous with the ridge line, wherein the press molding is formed on the top plate in the heated blank. A hot press characterized in that the portion is supported by the inner pad arranged so as to project from the top of the punch by a predetermined amount, and the punch is compacted by bringing the punch relatively close to the die. Manufacturing method of molded products.

The "hot press molded product" in the present invention is numerous as a component component of an automobile body or an automobile part. For example, a center pillar inner panel and a center pillar outer panel, a side sill inner panel and a side sill outer panel, an A pillar inner panel and an A pillar outer panel are used. , Roof rail inner panel, roof cloth, front side member and rear side member, and subframe (suspension member) and the like are exemplified.

According to the present invention, the non-temperature lowering portion (high temperature portion) of the portion formed on the vertical wall portion is enlarged by performing hot press forming using a punch and a die having an inner pad mounted freely on the top of the punch. This makes it possible to effectively eliminate the occurrence of cracks in the vertical wall.
Specifically, in the blank, the punch and the die are brought into contact with the inner pad attached to the top of the punch so that the top plate protrudes outward in the plan view in the pressing direction and the top plate has a step. By performing hot press forming using the above, it is possible to eliminate the occurrence of cracks in the portion formed on the vertical wall of the portion.

FIG. 1 is an explanatory diagram schematically showing a hot press apparatus according to the present invention and a press-molded product produced by these. FIG. 2 is an explanatory diagram schematically showing a hot press apparatus according to the present invention and a press-molded product produced by these. FIG. 3 is an explanatory diagram showing a situation in which a blank is hot-pressed using a conventional hot-pressing apparatus including a punch and a die. FIG. 4 is an explanatory diagram showing a situation in which hot press forming is performed on a blank using the hot press apparatus according to the present invention. FIG. 5 (a) is a numerical analysis of the plate thickness reduction rate distribution at the bottom dead center of the press-formed product shown in FIG. 9 (a) manufactured by a conventional hot press forming method without using an inner pad. FIG. 5 (b) is a contour diagram, in which FIG. 5 (b) is a position 4 mm above the bottom dead center of the press-formed product shown in FIG. 9 (a) manufactured by a conventional hot press forming method without using an inner pad. FIG. 5 (c) is a contour diagram obtained by numerical analysis of the temperature of each part of the above, and FIG. 5 (c) shows the molding of the press-formed product shown in FIG. FIG. 5 (d) is a contour diagram obtained by numerical analysis of the plate thickness reduction rate distribution at the dead center, and FIG. 5 (d) is shown in FIG. 2 (a) manufactured by the hot press forming method according to the present invention using an inner pad. It is a contour figure by numerical analysis of the temperature of each part at a position 4 mm above the bottom dead center of a press-molded product. FIG. 6A is an explanatory view showing the shape of the blank at a position 20 mm above the bottom dead center of molding when molding a hot press-molded product by the press molding apparatus according to the present invention, and FIG. 6B is an explanatory view. , It is explanatory drawing which shows the cross section of the press molding apparatus at this time. FIG. 7A is an explanatory view showing the shape of the blank at a position 20 mm above the bottom dead center of molding when the hot press-molded product is molded by the press molding apparatus according to the present invention described later, and is FIG. 7B. ) Is an explanatory view showing a cross section of the press molding apparatus at this time. FIG. 8A is a perspective view showing a hot press-formed product in which cracks occur, and FIG. 8B is an explanatory view showing a 1/2 cross section of a press-molding apparatus for the hot press-formed product. FIG. 9 (a) is a perspective view showing a hot press-formed product in which similar cracks occur, and FIG. 9 (b) is an explanatory view showing a 1/2 cross section of the press-molding apparatus of the hot press-formed product. 9 (c) is an explanatory view showing a cross section corresponding to the AA'cross section in FIG. 9 (a) in the press molding apparatus before the start of press molding. FIG. 10A is a contour diagram obtained by numerical analysis of the plate thickness reduction rate at the bottom dead point of molding in the hot press-molded product hot-press-molded by the press-molding apparatus shown in FIG. 8; ) Is a contour diagram obtained by numerically analyzing the temperature of each part at a position 10 mm above the bottom dead point of molding in the hot press-molded product hot-press-molded by the press-molding apparatus shown in FIG. 8 (c). FIG. 10D is a contour diagram obtained by numerical analysis of the plate thickness reduction rate at the bottom dead point of molding in a hot press-molded product hot press-molded by the press-molding apparatus according to the present invention. FIG. 10 (d) is a contour diagram of the present invention. FIG. 5 is a contour diagram obtained by numerically analyzing the temperature of each part at a position 10 mm above the bottom dead point of molding in a hot press-molded product hot-press-molded by the press-molding apparatus according to the above.

The present invention will be described with reference to the accompanying drawings.
1. 1. Hot press devices 11, 12 according to the present invention
FIG. 1 (a) is an explanatory view schematically showing a press-formed product 13 manufactured by the hot press device 11 according to the present invention, and FIG. 1 (b) is an explanatory view showing the hot press device 11 according to the present invention. It is explanatory drawing which shows. 2 (a) is an explanatory view schematically showing a press-formed product 14 manufactured by the hot press device 12 according to the present invention, and FIG. 2 (b) is an explanatory view schematically showing the hot press according to the present invention. It is explanatory drawing which shows the apparatus 12.

Hereinafter, the hot press devices 11 and 12 will be collectively described with reference to FIGS. 1 (a) and 1 (b), 2 (a) and 2 (b).

As shown in FIGS. 1 (b) and 2 (b), the hot press devices 11 and 12 include punches 15 and 16 which are dies for hot press and dies 17 and 18, and hot press. The device 11 further includes a blank holder 19.

The hot press device 11 uses the punch 15, the die 17, and the blank holder 19 to perform hot press forming on the blank 20 by drawing, so that the top plate 13a and the two ridges continuous to the top plate 13a are formed. It has a cross section (for example, a hat cross section or a grooved cross section) having 13b, 13b and two continuous vertical walls 13c, 13c on each of the two ridge lines 13b, 13b, and also has two ridge lines 13b, 13b and two vertical walls. A hot press-formed product 13 having a curved portion 13d in which at least one ridge line 13b and a vertical wall 13c of 13c and 13c project and bend to the outside of the top plate 13a in a plan view in the pressing direction is manufactured.

On the other hand, the hot press device 12 uses the punch 16 and the die 18 to perform hot press forming on the blank 20 by bending, so that the top plate 14a and the two ridge lines 14b and 14b continuous with the top plate 14a are formed. The top plate 14a has a cross section (for example, a hat cross section or a grooved cross section) having two vertical walls 14c and 14c continuous with each of the two ridge lines 14b and 14b, and the top plate 14a is in the height direction of the hot press molded product 14. A hot press-molded product 14 having a step 14e in the direction (direction substantially orthogonal to the top plate 14a) is manufactured. The top plate 14a is divided into a high-height portion and a low-height portion with the step 14e as a boundary, and the height changes at the step 14e.

The hot press dies according to the present invention are used for the punches 15 and 16. That is, the punches 15 and 16 include punch tops 15a and 16a and two punch shoulders R portions 15b and 16b continuous with the punch tops 15a and 16a.

In the hot press device 11, at least one of the two punch shoulder R portions 15b has a curved portion in a plan view in the pressing direction. This curved portion is for molding the curved portion 13d of the hot press molded product 13. FIG. 1 shows a cross section of the punch 15 at the position of the curved portion.

In the press-molded product 14 formed by the hot press device 12, the ridge line 14b formed by the two punch shoulder R portions 16b abuts against another vertical wall portion, and a step 14e is formed on the top plate 14a. FIG. 2B shows a cross section in the vicinity where the ridge line 14b formed by the punch shoulder R portion 16b abuts on another vertical wall portion, that is, a portion of the top plate 14a having a low height with a step 14e as a boundary.

The punches 15 and 16 include inner pads 21 and 21 arranged so as to project by a predetermined amount from the punch tops 15a and 16a in FIGS. 1B and 2B. The inner pads 21 and 21 are perpendicular to the pressing direction at a part of the portion of the blank 20 formed on the top plates 13a and 14a (the portion of the blank 20 formed on the vertical walls 13c and 14c near the punch shoulder R portion). It suffices to support the vicinity of the place where tension is applied in the direction of tension, but the remaining part (for example, all) excluding a part thereof may also be supported.

Accommodation holes 15c and 16c for accommodating inner pads 21 and 21 are bored in the punch tops 15a and 16a, and inner pads 21 and 21 are punched in the bottoms 15d and 16d of the accommodation holes 15c and 16c. Appropriate pressurizing mechanisms such as springs 15e and 16e and gas cushions are provided to project a predetermined amount from the tops 15a and 16a.

The inner pads 21 and 21 are arranged at the positions shown in FIGS. 1 (b) and 2 (b) at the start of press molding, and as the dies 17 and 18 approach the punches 15 and 16 after the start of press molding. It is urged by the dies 17 and 18 and gradually moves from the above positions toward the bottoms 15d and 16d of the accommodation holes 15c and 16c, and is completely accommodated in the punch tops 15a and 16a at the bottom dead center of molding and is completely contained in the punch tops 15a. , 16a are arranged so as to form a part of.

As shown in FIG. 1, it is preferable to use a die pad 17a supported by a die 17 or the like and sandwich the blank 20 between the die pad 17a and the inner pad 21. Further, in FIG. 2B, it is desirable to have a die pad as well (although not shown).
The hot press devices 11 and 12 according to the present invention are configured as described above.

2. 2. Manufacturing Method According to the Present Invention In the present invention, as shown in FIGS. 1 (a) and 1 (b), 2 (a) and 2 (b), a hot press device is applied to the heated blanks 20 and 20. Hot press-molded products 13 and 14 are manufactured by performing press-molding using 11 and 12.

FIG. 3 is an explanatory view showing a situation in which hot press forming is performed on a blank 20 using a conventional hot press device 30 including a punch 31 and a die 32, and FIG. 4 is an explanatory view showing a situation in which hot press forming is performed on a blank 20, and FIG. 4 is a hot press device according to the present invention. It is explanatory drawing which shows the situation of performing hot press forming on a blank 20 using 11 and 12.

As shown in FIG. 3, during the conventional hot press forming using the hot press device 30, the first portion 20a of the blank 20 is cooled by coming into contact with the die R portion 32a, and the second portion 20b is formed. Is cooled by contacting the punch shoulder R portion 31a. Therefore, in the blank 20, the third portion (the portion formed on the vertical wall in the press-molded product) 20c between the first portion 20a and the second portion 20b is a non-temperature lowering portion (a portion formed on the vertical wall in the press-molded product) in a narrow range. Since the strain is concentrated in the curved portion 13d or the formed portion (that is, 14d) of the curved portion 13d or the step 14e in the region (high temperature portion), the plate thickness is greatly reduced and cracks are likely to occur.

On the other hand, as shown in FIG. 4, in the present invention, the hot press forming of the top plate 14a on the top side having a low height with the curved portion 13d and the step 14e as the boundary is performed on the top plates 13a and 14a in the blank 20. By supporting the molded portion with an inner pad 21 arranged so as to project a predetermined amount of Ship from the punch tops 15a and 16a, the punches 15 and 16 are relatively close to the dies 17 and 18 and molded. , Will be done.

The first portion 20a of the blank 20 is cooled by contacting with the die-shaped R portions 17a and 18a, and the second portion 20b comes into contact with the inner pad shoulder R portion 21a instead of the punch shoulder R portions 15a and 16a. It is cooled by.

At this time, since the blank 20 is supported by the inner pad 21 at a position close to the dies 17 and 18 by a predetermined amount, the third portion 20a between the first portion 20a and the second portion 20b in the blank 20 is supported. 20c (a portion formed on a vertical wall in a press-molded product) 20c has a non-temperature lowering portion (high temperature portion) region formed in a wider range than the conventional example shown in FIG. The concentration of strain during molding at the molding location of 14e is alleviated, which reduces the plate thickness reduction rate and eliminates cracks.

FIG. 5A is a numerical analysis of the plate thickness reduction rate distribution at the bottom dead center of the press-formed product 2 shown in FIG. 9A, which was manufactured by a conventional hot press forming method without using an inner pad. 5 (b) is a contour diagram according to FIG. 5 (b), which is 4 mm above the bottom dead center of the press-formed product 2 shown in FIG. 9 (a), which is manufactured by a conventional hot press forming method without using an inner pad. FIG. 5 (c) is a contour diagram obtained by numerically analyzing the temperature of each part at the position, and FIG. 5 (c) shows a press-formed product 14 shown in FIG. 2 (a) manufactured by the hot press forming method according to the present invention using an inner pad. FIG. 5 (d) is a contour diagram obtained by numerical analysis of the plate thickness reduction rate distribution at the bottom dead center of molding, and FIG. 5 (d) is FIG. 2 (a) manufactured by the hot press forming method according to the present invention using an inner pad. ) Is a contour diagram obtained by numerical analysis of the temperature of each part at a position 4 mm above the bottom dead center of the press-formed product 14.

As can be understood from the comparison of FIGS. 5 (b) and 5 (d), the present invention presents the present invention at a position 4 mm above the bottom dead center of the molded product 14 of the press-molded product 14 as compared with the conventional example. The non-temperature lowering portion (high temperature portion) of the portion formed on the vertical wall 14c is enlarged.

Therefore, as shown in FIGS. 5 (a) and 5 (b), in the conventional example, the plate thickness reduction rate of the vertical wall 14c of the stepped portion of the press-formed product 14 reaches 28.9%, which indicates cracking. However, in the present invention, this plate thickness reduction rate is suppressed to 18.6%, and it can be seen that cracks do not occur in the vertical wall 14c of the stepped portion.

13 Hot press molded product 15 Hot press die 15a Punch top 15b Punch shoulder R part 20 Blank 21 Inner pad

Claims (5)

A punch top, a punch shoulder R portion continuous with the punch top, and an inner pad that is arranged so as to project from the punch top to the outside of the punch top by a predetermined amount and is housed in the punch top at the bottom dead center of molding. With punches, including
A die that hot presses a blank in cooperation with the punch,
During the hot press working, a free end arrangement space forming portion for making the outer peripheral edge portion an unconstrained free end until the outer peripheral edge of the blank is sandwiched between the punch and the die.
With
The punch and the die form the blank into a hot press molded product by the hot press working.
The hot press-formed product includes a groove-shaped cross section having a top plate, a pair of ridge lines provided on the top plate, and a pair of vertical walls continuous with the corresponding ridge lines, respectively. The punch so that both ends of the groove-shaped cross section in the extending direction of the ridge have a shape that is open toward the extending direction of the ridge, and the pair of ridges have a bent portion in the middle. And the die is formed and arranged ,
The punch and the die are used to form a hot press-molded product including a top plate, a ridge line provided on the top plate, and a vertical wall continuous with the ridge line and extending so as to intersect the die. The blank is configured to be hot pressed
The punch top is provided as a portion forming the top plate.
The punch shoulder R portion is provided as a portion forming the ridgeline.
The punch further includes a portion that is continuous with the punch shoulder R portion and forms the vertical wall.
The inner pad is arranged adjacent to the portion forming the vertical wall, and the inner pad is arranged.
The inner pad is arranged at a position where the edge of the top of the punch protrudes to the outside of the punch and is bent in a plan view in the hot press direction.
A hot press in which the inner pad is not arranged at a position outside the bent portion of the edge of the punch top in a plan view in the hot press direction, which protrudes to the outside of the punch. Mold for use. A die pad, which is arranged so as to project a predetermined amount from the recess formed in the die toward the punch side and is housed in the recess at the bottom dead center of molding.
With more
The hot press according to claim 1, wherein the hot press working is performed by relatively moving the punch top and the die with the die pad and the inner pad sandwiching the blank. Mold. The hot press die according to claim 1 or 2 , wherein flanges are not formed at both ends of the grooved cross section in the extending direction of the ridgeline . A hot press apparatus comprising the hot press die according to any one of claims 1 to 3 . Manufacture of a hot press-molded product, which comprises performing hot press molding on a heated blank using the hot press die according to any one of claims 1 to 3. Method.

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